cdf77, welcome to Flyertalk and the BA board.

I'm not sure what the minimum connection time is for US Preclearance at Dublin, but I can imagine that 1h25 is probably approaching the limit.

For connections, you can safely ignore the dire warnings about arriving 3.5 hours in advance. That was in place when the airport was chronically understaffed in security, having to perform extra swab tests because it failed an EU audit, and as a consequence was managing queues of people for both check-in desks and security that stretched into tensabarriers outside the terminal. If you stay airside (or even have to go landside temporarily) you avoid all of that and normal MCTs apply.

In this circumstance, if you still meet the MCT even with the new flight times then BA will not re-book you for free. If you don't, then they will make the necessary change to your booking when eventually it reaches the top of the priority pile - which could be some time. You should then also have a full choice of what the itinerary looks like, so you can play with different times or perhaps even get a direct flight from London - although this will be harder to argue given you only have a flight re-timing, not a cancellation.

I would probably ring sooner rather than later if you want peace of mind. The LHR passenger cap, which seems to be a policy with no defined end, means BA may yet still have to cancel some November DUB services and consolidate, so what looks available now may not be in a month's time.